Concrete pipes, earthern pipes, iron pipes, etc. have been used as service or sewage water pipes, drain pipes or agricultural water pipes. However, these pipes involve a drawback of easily suffering from corrosion in contact with acids, salts or oils and fats. In view of the above, lining layers comprising synthetic resins such as unsaturated polyester resin, vinyl ester resin, urethane modified (metha)acrylate resin, etc. as a binder in admixture with inorganic aggregates are formed to the inner surface of pipes and used as inner lined pipes (inner lined pipes as described in, for example, Japanese Patent Laid Open Sho 60-90713).
As a method of manufacturing inner lined pipe, there has been known a centrifugal molding method as shown in Japanese Patent Laid Open Sho 50-76174.
FIG. 8 is a schematic explanatory view of an apparatus used for such a method in which a pipe 1 to be lined is placed on rotating rollers 2 . . . and the rotating roller 2 is driven by a driving device (not illustrated) to exert a centrifugal force of greater than several tens of g (by gravitational unit) to the inner circumferential surface of the pipe 1. Lining material scattered from a lining material discharge nozzle 32 to the inner circumferential surface of the pipe is smoothed by the centrifugal force upon reaching the inner circumferential surface of the pipe. The device for supplying the lining material comprises rails 4 laid in parallel with the longitudinal direction for the axis of the pipe 1, a carrier 3 placed movably horizontally thereover and an arm member 31 is attached to the carrier 3 on the side of the pipe 1, retractably in the longitudinal direction of the pipe axis at the inside of the pipe 1, and the lining material discharge nozzle 32 is disposed at the top end of the arm member 31. The discharge nozzle 32 is connected by way of a lining material supply pipe 33 to a hopper 34 on the carrier 3, and a resin mortar R.sub.1 (mixture of resin material and inorganic aggregate) and a hardening agent H.sub.1 previously mixed are stored in the hopper 34. The stored lining material is supplied by means of air pressure, etc. of a compressor 35 by way of the supply pipe 33 to the discharge nozzle 32. The lining material is sprayed from the discharge nozzle 32 to the inner circumferential surface of the pipe 1 and smoothed by the rotational centrifugal force of the pipe 1 to form a hardened lining layer. Accordingly, by gradually advancing the arm member 31 deeply to the inside of the pipe 1, the lining layer is formed to the circumferential surface over the entire length thereof.
By the way, since the resin mortar as the lining material is previously mixed with the hardening agent before discharge from the discharge nozzle 32, the lining material should have a long pot life. If the selection of the material is not proper, the material hardens in the supply pipe 33 or the discharge nozzle 32 to result in clogging troubles. Further, if clogging does not occur, since the lining material which starts hardening and gradually loses flexibility is supplied to the inner circumferential surface of the pipe 1, it is necessary to considerably increase the centrifugal force or use an additionally physical smoothing means (for example, spatula, etc.) in order to smooth the material. This inevitably lowers the production efficiency and the material once mixed with the hardening agent has to be spent completely soon, which may lead to wasteful consumption of the lining material.
On the other hand, although the lining material is spread and coated to the inner circumferential surface of the pipe by the centrifugal force of the pipe, the lining material is not firmly adhered to the inner circumferential surface of the pipe 1, depending on the material and the smoothness at the inner circumferential surface of the pipe and, accordingly, the inner lined layer may sometime be peeled off readily by internal stresses caused by the difference in heat shrinkage or external load applied from the outside because of the insufficiency in the adhesion.
As a means for overcoming such problems, Japanese Patent Laid Open Sho 58-78618 discloses a technique of disposing a grinding means at the top end of the arm member 31 for roughening the circumferential surface of the pipe. However, the technique makes the apparatus complicate and, nevertheless, can not completely overcome the foregoing problem and, in addition, results in an additional problem of lowering the production efficiency due to the increase in the production steps.